The field of the invention relates to magnetic resonance spectroscopy (MRS) and more particularly to magnetic resonant imaging (MRI).
MRS and MRI systems are known. Both are systems which are capable of measuring a quantity of a particular atom in other larger structures, such as a test tube or the human body. MRS is typically devoted to detecting a spectral distribution of resonance frequencies of a particular atom. MRI possesses the additional capability of combining a series of measurements to create an image of the distribution and quantity of the measured atom.
Both MRS and MRI rely on externally generated magnetic fields for purposes of aligning a nuclei of a particular atom of interest. The aligned atoms of MRS and MRI systems are subjected to a pulse of radio frequency (rf) energy, which radio frequency may be absorbed only by the nuclei of the atom of interest. Following the pulse, the radio frequency energy may be absorbed and emitted by the nuclei of the atom. Rf receivers placed close to the test sample look for and measure a level of the released energy, the magnitude of which release provides a measure of the quantity of the atoms of interest present.
The frequency at which a nuclei of an atom will absorb energy is referred to as its resonant frequency. At its resonance frequency, a nuclei of an atom may simultaneously absorb and emit energy.
The frequency at which an atom will resonate depends upon the type of atom and upon the magnetic field to which the atom is subjected. The resonant frequency within a particular magnetic field is referred to as the atom""s Larmor frequency.
One atom that is of particular usefulness in MRS and MRI is hydrogen. At a magnetic field of 1.5 Gauss, hydrogen is known to have a Larmor frequency of approximately 64 MHZ. Hydrogen has a relatively large nuclear magnetic moment. It also has a relatively large concentration in humans. These two factors have made hydrogen a relatively important element in magnetic resonant imaging.
In creating images, a set of gradient coils are typically used to create a magnetic gradient across an imaging field of the MRI system. The gradient is important because it also creates a gradient in the Larmor frequencies of atoms lying within the imaging fields. With a prior knowledge of the magnetic gradient, a MRI operator can select a frequency of the rf pulse for a particular location within the imaging field knowing that only atoms at that location within the magnetic field would have the Larmor frequency which would resonate at the selected frequency.
While hydrogen is an important imaging element, it is not an element directly related to oxidative metabolism. Oxygen is an element more closely related to metabolism, but which is much harder to detect than hydrogen. Hydrogen is known to have a magnetic moment over 7 times larger than oxygen. Further, as a result of metabolism, oxygen becomes combined with hydrogen to produce a water molecule which further complicates detecting oxidative metabolism by hydrogen MRI. Accordingly, a need exists for a means of detecting oxygen which is not effected by the molecular status of the oxygen.
A method and apparatus are provided for enhancing a signal quality from a first atom of a pair of spinxe2x80x94spin coupled atoms, in a magnetic resonance imaging system. The method includes the steps of exciting the first atom of the pair of spinxe2x80x94spin coupled atoms within the magnetic resonance imaging system at a Larmor frequency of the first atom and exciting the second atom at the Larmor frequency of the second atom. The method further includes the step of detecting a signal from the first atom.